They are working on a complete change to the cloud platform. The docs that you have linked to have to do with that new platform. But it’s not what you need in order to use the code that you will find in this forum. That code is published through the “IDE,” The old “integrated development environment” used for groovy. The name has now been changed to the “groovy IDE.”
As far as I know, all of the instructions in the custom code FAQ still apply.
But I will leave any follow on to some of the people who are actually doing The coding.
Since you are trying to get the hive code working, I suggest you ask your question in that thread. The original author will be automatically notified when a new post is added to that thread and other people who are using the code will also be able to help.
But ignore all of the new documentation that you found other than the custom code FAQ. That all goes with the new platform, and it’s not how you will install current groovy code.
None of the confusion is your fault, of course – – they have been releasing bits and pieces of the new platform without fully documenting either what it is or when you should use it, and everybody is getting confused.